Radial piston machine

ABSTRACT

A radial piston machine wherein the cylinder block rotates about a stationary pintle having in its external surface a highpressure chamber and a low-pressure chamber, and wherein the cylinder block has radially outwardly extending cylinder bores travelling seriatim in register with the chambers and with lands provided on the pintle between the two chambers. The lands of the pintle are provided with recesses in the form of cutouts or cavities which are in temporary communication with successive cylinder bores when the cylinder block rotates so that the pressure fields which develop in the region of the recesses communicating with cylinder bores containing pressurized fluid oppose radial movements of the cylinder block. The recesses in the lands of the pintle can be replaced by or provided in addition to recesses in the internal surface of the cylinder block.

United States Patent 1 1 [111 3,874,272 Bosch i 51 Apr. 1, 1975 RADIALPISTON MACHINE Primary ExaminerWilliam L. Freeh [75] Inventor. PaulBosch, Ludwigsburg, Germany Attorney g or Firm MiChael S. Striker [73]Assignee: Robert Bosch GmbH, Stuttgart,

Germany 22 Filed: July 18, 1973 ABSTRACT [21] Appl. No.: 380,164 Aradial piston machine wherein the cylinder block rotates about astationary pintle having in its external surface a high-pressure chamberand a low-pressure [30] Forelgn Apphcamn Priority Data chamber, andwherein the cylinder block has radially July 22, 1972 Germany .i 2236125outwardly extending Cylinder bores travelling Seriatim in register withthe chambers and with lands provided [52] US. Cl. 91/498 the pintlebetween the two Chambers The lands of [51] lllt. Cl. F0lb 13/06 thepintle are p i with recesses i the f of [58] Fleld of Search 91/487,485, 6.5, 507 cutouts or cavities which are in temporary communi cationwith successive cylinder bores when the cylin- [56] References C'ted derblock rotates so that the pressure fields which de- UNITED STATESPATENTS velop in the region of the recesses communicating 2.9445297/1960 Wiggermann 9l/6.5 with cylinder bores containing pressurizedfluid op- 3()82.696 3/1963 Henrichsen 91/487 pose radial movements ofthe cylinder block. The re- 3.i7i,36i 3/1965 Boulet 91/487 cesses in thelands of the pintle can be rep1aced or g I 5%3 provided in addition torecesses in the internal surface 1mm 3,520,229 7/1970 Slimm et a1 .79l/6.5 of the cylmder blocki FOREIGN PATENTS OR APPLICATIONS UnitedKingdom 91/498 14 Claims, 6 Drawing Figures FHENTEU APR 1 19?? SHEET 1OF 2 RADIAL PISTON MACHINE BACKGROUND OF THE INVENTION The presentinvention relates to radial piston machines, and more particularly toimprovements in radial piston machines of the type wherein a cylinderblock having radially extending cylinder bores rotates about astationary valve or pintle whose periphery is provided with ahighpressure chamber and a low-pressure chamber.

It is already known to provide a radial piston machine with a pintlehaving in its external surface two arcuate chambers separated from eachother by lands. The inner end portions of the cylinder bores orbit alonga path which is adjacent to the chambers and to the lands so that eachcylinder bore communicates first with one of the chambers, thereupontravels along one of the lands, then communicates with the otherchamber, thereupon travels along the other land, and again communicateswith the one chamber. A drawback of presently known radial pistonmachines of the just outlined character is that the forces which developwhen a piston moves in the cylinder block radially inwardly, i.e.,toward the inner end portion of the respective cylinder bore, tend toflex the pintle away from the respective inner end portion andsimultaneously tend to move the adjacent portion of the cylinder blockradially of and away from the pintle. At the same time, the portion ofthe cylinder block which is located opposite the piston dwelling in itsinner end position tends to move nearer to the adjacent portion of theexternal surface on the pintle. While the liquid which fills theclearance between the internal surface of the cylinder block and theexternal surface of the pintle opposes such radial displacements of thecylinder block, its resistance is not always sufficient to insureaccurate centering of the cylinder block so that pressurized liquid islikely to leak in the region where a piston assumes its inner endposition and the losses due to friction between the cylinder block andthe pintle opposite such region are extremely high.

It is further known to reduce the effect of forces which tend to movethe cylinder block radially of the pintle by providing the lands betweenthe high-pressure and low-pressure chambers of the pintle with recessesin the form of cutouts or cavities. The pintle contains a system ofvalve elements serving to connect the higher-pressure chamber with therecess or recesses which are located opposite a piston in its inner endposition. This results in the establishment of highpressure fields whichare capable of counteracting some but not all of the forces tending tomove the cylinder block radially of the pintle. In addition tounsatisfactory neutralization of radial forces, the just describedradial piston machine exhibits the serious drawback that the valveelements in the pintle contribute excessively to the initial andmaintenance cost of the machine. The maintenance cost is high becausethe channels wherein the pressurized fluid flows between thehigh-pressure chamber and selected recesses are likely to be clogged byimpurities in the fluid to thereby reduce the effectiveness of thecentering action upon the cylinder block and to cause excessive wearupon the neighboring surfaces of the cylinder block and pintle.

SUMMARY OF THE INVENTION An object of the invention is to provide anovel and improved radial piston machine wherein the forces tending tomove the cylinder block radially of the pintle are balanced orneutralized with greater accuracy and with a higher degree ofreliability than in presently known machines.

Another object of the invention is to provide a novel and improvedpintle and a novel and improved cylinder block for use in radial pistonmachines of the just outlined character.

A further object of the invention is to provide a radial piston machinewhose pintle and cylinder block are simpler than in the aforementionedradial piston machines wherein the pintle is provided with valveelements, and wherein the balancing of radial forces acting on thecylinder block is achieved in a simpler, less expensive and morereliable way than in heretofore known machines.

An additional object of the invention is to provide a radial pistonmachine wherein the radial forces acting on the cylinder block areneutralized to such an extent that the combined area of surfacesprovided on the pintle and serving to guide the cylinder block can bereduced sufficiently to greatly reduce losses due to fric tion when thecylinder block is caused to rotate relative to the pintle.

Still another object of the invention is to provide a radial pistonmachine which can stand longer periods of use than heretofore knownmachines because the wear upon the neighboring surfaces of the cylinderblock and pintle iswa' small fraction of such wear in conventionalmachines, and wherein the leakage of fluid between the cylinder blockand the pintle is a small fraction of leakage in presently knownmachines.

One feature of the invention resides in the provision of a radial pistonmachine which can be used as a pump or as a motor and comprises a rotarycylinder block having a cylindrical internal surface and radiallyextending equidistant cylinder bores including end portions (e.g., inthe form of round ports) terminating in the internal surface of theblock, and a stationary valve or pintle having a cylindrical externalsurface surrounded by the internal surface of the cylinder block, ahigh-pressure chamber and a low-pressure chamber machined into theexternal surface in such positions as to register with and to be sweptseriatim by the end portions of successive cylinder bores when thecylinder block rotates relative to the valve. The external surface ofthe valve includes two portions which constitute lands between the twochamber, and the lands are providcd with recesses in the form of cutoutsor cavities which are offset relative to the chambers, as considered inthe axial direction of the cylinder block. Each recess is in temporarycommunication with that cylinder bore whose end portion travels in theregion of the respective land whereby the pressure fields which developin the recesses communicating with the high-pressure chamber (by way ofthe end portions of the cylinder bores) are capable of at leastpartially counteracting the radial forces which tend to move thecylinder block toward or away from the valve.

The aforementioned recesses are more effective than the valve elementsin the pintles of conventional radial piston machines but theirmachining into the external surface of the valve can be carried out at afraction of the cost of such valve elements.

Another feature of the invention resides in the provision of recesses inthe form of cavities or cutouts which are machined into the internalsurface of the cylinder block to perform substantially the same functionas the recesses in the lands of the valve. The recesses in the cylinderblock can be provided in addition to or as a substitute for recesses inthe lands of the valve.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved radial piston machine itself, however, both as of itsconstruction and its mode of operation, together with additionalfeatures and advantages thereof, will be best understood upon perusal ofthe following detailed description of certain specific embodiments withreference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING the cylinder block substantially asseen in the direction of arrow V in FIG. a.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIGS. I and2, there is shown a radial piston machine which comprises a housing 1provided with a separable cover or lid 2. The cover 2 is formed with abore 3 for a cylindrical valve or pintle 4 which is secured to the coverby means of a pin 3a. The pintle 4 is surrounded by a cylinder body orblock 5 which is rigid (e.g., integral) with a shaft 7. The shaft 7 isdriven by thc bloek 5 when the machine is operated as a motor, and theshaft 7 drives the block 5 when the machine is operated as a pump. Ashoulder of the block 5 abuts against a bearing 6 mounted in the housing1 and surrounding the shaft 7.

The block 5 is provided with radially extending cylinder bores 8 forpistons or plungers 9 each of which has a shoe l0 abutting against thecylindrical internal surface of a floating control ring 11 whichsurrounds the block 5. The pistons 9 are reciprocable in the respectivecylinder bores 8 with minimal clearance. The inner part ofcach cylinderbore 8 is surrounded by a conical surface 12 and terminates in acircular end portion or port 13 as well as in two grooves 14, 15 whichare disposed diametrically opposite each other with reference to thecenter of the respective port 13 and are located in a plane whichincludes the common axis of the cylinder block 5 and pintle 4.

The means for changing the position of the control ring 11 radially ofthe block 5 and for thereby changing the strokes of the pistons 9comprises a nut 16 which is secured to and extends radially outwardlyofthe control ring 11, a spindle 17 which meshes with the nut 16 and isrotatable in a bell I8 ofthe housing I, and a hand wheel 19 which issecured to the outer end portion of the spindle 17. The latter is heldagainst axial movement so that, when the hand wheel 19 is rota ed, thenut 16 moves the control ring 11 radially oft e cylinder block 5 andthereby changes the strokes of the pistons 9. A helical spring 20 reactsagainst the housing 1 and biases the control ring 11 upwardly, as viewedin FIG. 1, i.e., in the axial direction of the spindle 17.

The pintle 4 is formed with two axially parallel holes 23, 24 one ofwhich terminates in an inlet and the other of which terminates in anoutlet for a fluid medium, e.g., oil. The inner end portions of theholes 23, 24 respectively communicate with arcuate control chambers 21,22 which are machined into the cylindrical external surface of thepintle 4 and register with the cylinder bores 8. Thus, when the cylinderblock 5 rotates about the pintle 4, successive ports 13 sweep past thecontrol chambers 21, 22 so that the pistons 9 can draw fluid into therespective cylinder bores 8 while moving radially outwardly and that thepistons can expel fluid from the respective bores 8 during movementtoward the axis of the pintle 4. The control chambers 21, 22 are ofidentical length, as considered in the circumferential direction of thepintle 4, and are separated from each other by two axially parallellands 29, best shown in FIG. 2. Each of the lands 29, 30 constitutes aportion of the cylindrical external surface of the pintle 4. The controlchamber 21 is flanked by two narrow sealing ribs 25, 26 which extend inthe circumferential direction of the pintle 4 between the lands 29, 30,and the control chamber 22 is flanked by two similar sealing ribs 27,28. The width of the control chamber 21 and sealing ribs 25, 26respectively equals or approximates that of the control chamber 22 andsealing ribs 27, 28.

In accordance with a feature of the invention, the land 29 between thecontrol chambers 21, 22 is provided with four substantially rectangularrecesses in the form of cutouts or cavities 31, 32, 33 and 34 which arerespectively provided with narrow and short channels or extensions 35,36, 37, 38. The extensions 37, 38 are adjacent to the path of successivegrooves 14 and the extensions 35, 36 are adjacent to the path ofsuccessive grooves 15. The arrow A denotes in FIG. 2 the direction inwhich the cylinder block 5 rotates relative to the periphery of thepintle 4. The cutouts 31, 32 are outwardly adjacent to the sealing ribs25, 27 and the cutouts 33, 34 are outwardly adjacent to the sealing ribs26, 28. The arrangement is such that successive ports 13 and thecorresponding grooves l4, 15 can establish communication between thecontrol chamber 21 and cutouts 31, 33 and thereupon between the controlchamber 22 and cutouts 32, 34. The pintle 4 is further provided with afirst auxiliary sealing rib 31 which is outwardly adjacent to thecutouts 31, 32 and merges into the land 29, and with a second auxiliarysealing rib 33 which is outwardly adjacent to the cutouts 33, 34 andalsomerges into the land 29. The length of each of the extensions 35-38,considered in the axial direction ofthe pintle 4 (i.e., vertically, asviewed in FIG. 2), may but need not equal the corresponding dimension ofthe groove 14 or 15.

The land 30 between the control chambers 22, 21 is also provided withfour recesses in the form of cutouts or cavities 39, 40, 41, 42 whichrespectively communicate with channels in the form of small bores 49,45, 50, 46. The cutouts 39, are outwardly adjacent to the sealing ribs25, 27 and the cutouts 41, 42 are outwardly adjacent to the sealing ribs26, 28 (as considered in the axial direction of the pintle 4). Thecutouts 40 and 42 are respectively located behind the cutouts 39, 41, asconsidered in the direction of rotation of the cylinder block 5 (arrowA).Thc bores 46, 50 are respectively provided with inlets 44, 48 whichare adjacent to the path of movement of successive grooves 14, and thebores 45, 49 respectively have inlets 43, 47 which are adjacent to thepath of movement of successive grooves 15. An auxiliary sealing rib 39of the pintle 4 is outwardlyadjacent to the cutouts 39, 40, and asimilar auxiliary sealing rib 41' is outwardly adjacent to the cutouts41, 42. The auxiliary sealing ribs 39, 4] merge into the land 30. Thebores 45, 46 can cooperate with successive ports 13 and the associatedgrooves 14, l5 to establish communication between the control chamber 22and the cutouts 40, 42. The bores 49, 50 can cooperate with successiveports 13 and the associated grooves 14, to establish communicationbetween the control chamber 21 and the cutouts 39, 41. Thus, successivegrooves 14 and the corresponding ports 13 will connect first the chamber22 with the cutout 42 and thereupon the chamber 21 with the cutout 41,and successive grooves 15 and the associated ports 13 will connect thechamber 22 first with the cutout 40 and thereupon the chamber 21 withthe cutout 39.

The control chamber 21 communicates with a tapering triangular pilotnotch 51 which extends into the land and insures a gradually increasingcommunication between successive ports 13 and the chamber 21 when thecylinder block 5 rotates. The control cham ber 22 communicates with asimilar tapering triangular pilot notch 52 which extends into the land29 and insures a gradually increasing communication between successiveports 13 and the chamber 22. The length of the pilot notch 51 (asconsidered in the circumferential direction ofthe pintle 4) is selectedin such a way that a port 13 begins to communicate with the controlchamber 21 only after the corresponding grooves 14,

15 have moved beyond the inlets 44, 43 of the bores 46, 45. Analogous,the length of the pilot notch 52 is such that a port 13 begins tocommunicate with the control chamber 22 only after the respectivegrooves 14, 15 have advanced beyond the extensions 37, of the cutouts33, 31. As shown in FIG. 2, the grooves 14, 15 are positioned in such away that the groove 14 respectively communicates with the extensions 37,38 when the associated groove 15 registers with the extensions 35, 36,and that the groove 14 respectively rcgisters with the inlets 44, 48when the groove 15 respec tively registers with the inlets 43, 47.

The operation:

When the cylinder block 5 rotates in the direction indicated by arrow A,the end portions or ports 13 of successive cylinder bores 8 orbit aboutthe axis of the pintle 4 and sweep seriatim along the control chamber21, land 29, control chamber 22, land 30, control chamber 21, etc. Byfollowing the orbital movement of a single port 13 and the associatedgrooves 14, 15, it will be seen that, when the port 13 reaches the land29, the grooves 14, 15 respectively move into register with theextensions 37, 35 before the port 13 moves beyond the control chamber21, i.e., the port 13 and the associated grooves 14, 15 establishcommunication between the control chamber 21 and the cutouts 31, 33. Thecommunication between the control chamber 21 and Cutouts 31, 33 is ofshort duration but suffices toinsure an equalization of pressure offluid in the chamber 21 and cutouts 31, 33. 1f the control 21 isconnected to the suction (low-pressure) opening of the pintle 4, thepressure in the cutouts 31,33 increases negligibly so that pressurefields developing in the region of these cutouts do not contributesignificantly to balancing of forces which tend to move the cylinderblock 5 radially of the pintle 4.

As the cylinder block 5 continues to rotate, the port 13 and theassociated grooves 14, 15 respectively move out of register with thecontrol chamber 21 and cutouts 33, 31. At such time, the correspondingpiston 9 changes the direction ofits movement in the respective cylinderbore 8. The port 13 then reaches the pilot notch 52 and thus begins tocommunicate with the control chamber 22 which contains pressurizedfluid. Thus, there begins to take place an equalization of pressuresbetween the interior of the chamber 22 and the adjacent bore 8. Shortlythereafter, the grooves 14, 15 respectively reach the extensions 38, 36so that the cutouts 34, 32 receive pressurized fluid and the pressuretherein rises to a maximum vallue at the time when the port 13 is infull or substantial register with the control chamber 22 but the grooves14, 15 continue to comm unicate with the extensions 38, 36. When thegrooves 14, 15 respectively advance beyond the extensions 38, 36, thepressure of fluid in the cutouts 34, 32 gradually decreases due toleakage of fluid between the periphery of the pintle 4 and the cylinderblock 5. The pressure of fluid in the cutouts 34, 32 riises again whenthe next groove 15 begins to communicate first with the pilot notch 52and thereupon directly with the control chamber 22.

When the port 13 begins to advance beyond the control chamber 22, thegrooves 1.4, 15 respectively communicate with the inlets 44, 43 of thebores 46, 45 before the communication between the control chamber 22 andport 13 is interrupted. There takes place an.

equalization ofpressures between the control chamber 22 and the cutouts42, which respectively communicate with the bores 46, 45. The pressurein the cutouts 42, 40 begins to decrease as soon as the grooves 14, 15respectively advance beyond the inlets 44, 43, i.e., as soon as the port13 is sealed from the bores 46, 45. The same procedure is repeated whenthe next port 13 begins to advance beyond the control chamber 22 so thatthe grooves 14, 15 which are associated with the next port 13 move pastthe inlets 44,43.

The port 13 moves along the land 30 when the corresponding piston 9reaches the inner end of its stroke. The pressurized fluid in thecutouts 42, 40 then balances theforce which tends to urge the cylinderblock 5 against the pintle 4 whenever a piston 9 reaches the inner endof its stroke, The drop offluid pressure in the cutouts 42, 40 is slowerthan in the cutouts 34, 32 which are disposed diametrically opposite thecutouts 42, 40 with reference to the axis of the pintle 4. This is dueto the fact thatthe clearance between the cylinder block 5 and thepintle 4 in the region of the cutouts 42 40 is smaller than in theregion of the cutouts 34, 32. Consequently, the fluid in the cutouts 42,40 can, on the average, offer a greater resistance to radialdisplacement of the cylinder block 5 than the fluid in the cutouts 34,32. The widths of the gaps between the cylinder block 5 and pintle 4automatically assume such values that the forces acting On the pintle 4balance or neutralize each other.

When the port 13 advances beyond the control chamber 22, it moves intoregister with the pilot notch 51 of the control chamber 21. In themeantime, the corresponding piston 9 has changed the direction of itsmovement so that it travels radially outwardly to draw fluid into therespective bore 8. The pressure in the bore 8 begins to approach that inthe control chamber 21 and the cutouts 41, 39 begin to receive fluidfrom the control chamber 21 by way of the port 13, grooves 14, 15,inlets48, 47 and bores 50, 49. The pressure fields in the region of thecutouts 41, 39 correspond to those in the region of the cutouts 33, 31,i.e., they are relatively weak and do not offer a substantial resistanceto radial displacement of the cylinder block 5. When the grooves 14, 15advance beyond the inlets 48, 47, the cylinder block has completed onefull revolution.

It will be noted that the pressure fields in the region of the cutoutsat one end of the control chamber 21 or 22 develop subsequent todevelopment of such pressure fields in the region of cutouts at theother end of the respective control chamber. In spite of continuousfluctuations of fluid pressure in the cutouts, the arrangement of FIG. 2insures a highly satisfactory neutralization of forces which act uponthe pintle 4 and further insures that the pressure fields in the regionof cutouts are capable of withstanding the tendency of the cylinderblock 5 to move radially of the pintle. Due to the aforedescribedsymmetric distribution of cutouts with reference to the axis of thepintle 4, the machine operates satisfactorily irrespective of thedirection of rotation of the cylinder block 5 and irrespective ofwhether the control chamber 21 or 22 contains pressurized fluid.

Another advantage of the structure shown in FIG. 2 is that the pressurefields in the region of cutouts can stand substantial radial forceswhich tend to move the cylinder block 5 relative to the pintle 4 andwhich tend to flex the pintle so that the combined area of the sealingribs 25-28, lands 29, 30 and auxiliary sealing ribs 31, 33, 39', 41 canbe made small. This reduces the losses due to friction.

The cutouts or recesses 31-34 and 39-42 form two groups of cutouts oneof which is provided in the land 29 and the other of which is providedin the land 30. Each group comprises two cutouts (31, 33 and 40, 42)which can communicate with successive cylinder bores 8 before such borescommunicate with the other two cutouts (32, 34 and 39, 41 All of thecutouts are offset relative to the control chambers 21, 22, asconsidered in the axial direction of the pintle 4.

FIG. 3 illustrates the cylindrical external surface of a modified valveor pintle 104. The control chambers are shown at 56 and 57, the narrowsealing ribs for the chambers 56 and 57 at 58, 59 and 60, 61, and thelands at 62 and 63. The land 62 is provided (as considered in thedirection of arrow A) with recesses or cutouts 64, 65 having channels orextensions 70, 71 located in the path of movement of successive grooves14, and

with recess or cutouts 66. 67 having channels or extensions 72, 73located in the path of movement of successive grooves 15. The cutouts64, 66 can communicate with the control chamber 56 and the cutouts 65,67 can communicate with the control chamber 57. The auxiliary sealingribs for the cutouts 64, 65 and 66, 67 are respectively shown at 68 and69. The length of the extensions 70, 71 and 72, 73, as considered in thecircumferential direction of the pintle 104, is selected in such a waythat they can register fully or to a substantial extent with the grooves14 and 15.

The land 63 of the pintle 104 is provided with recesses or cutouts 74,76 which can communicate with the control chamber 57 by way of theirchannels or extensions 78, 80, successive grooves 14, 15 and thecorresponding ports 13. The land 63 is further provided with recesses orcutouts 75, 77 having channels or extensions 79, 81 which cancommunicate with the control chamber 56 by way of successive grooves 14,15 and the associated ports 13. The pilot notches of the chambers 56, 57are respectively shown at 84 and 85. The auxiliary sealing ribs for thecutouts 74, and 76, 77 are respectively shown at 82 and 83. Theextensions 70, 7l, 78, 79 and 72, 73, 80, 81 begin to communicate withthe respective grooves 14, 15 when the corresponding ports 13 are stillin some communication or begin to communicate with the respectivecontrol chamber 56, 57. Thus, the length of intervals during which thecutouts communicate with the respective control chambers is relativelyshort.

it will be noted that the pilot notches 84, 85 taper counter to thedirection (arrow A) of rotation of the cylinder block (not shown in FIG.3). The length of pilot notches 84, 85 is selected in such a way that,when a port 13 travels for example toward the control chamber 57 (seethe position of the port 13 in FIG. 3), the corresponding grooves l4, 15move beyond the extensions 70, 72 before the port 13 reaches the tip ofthe pilot notch 85. The same applies for the extensions 78, 80 and thepilot notch 84.

The distance between the extensions 71, 78 or the extensions 73, 80which can be communicatively connected to the chamber 57 is a wholemultiple of the distance between the centers of two neighboring ports 13in the cylinder block, as considered in the circumferential direction ofthe pintle 104. The same applies for the extensions 79, 70 or 81, 72which can communicate with the control chamber 56. The remainder of thehydraulic machine which embodies the pintle 104 of FIG. 3 is assumed tobe identical with that of the machine shown in FIG. 1.

The sequence in which the pressure fields develop in the region ofcutouts 64-67 and 74-77 is analogous to that for the pressure fields inthe region of cutouts shown in FIG. 2. In contrast to the operation ofthe embodiment of FIGS. 1-2, the equalization of pressure in all cutoutswhich are associated with the control chamber 56 or 57 takes placesimultaneously. The pressure fields which develop in the region of thecutouts 65, 74 resp. 67, 76 which can be connected to the controlchamber 57 are spaced apart a distance which is less than considered inthe circumferential direction of the pintle 104. Therefore, suchpressure fields have components which are added to each other and act indirections normal to a symmetry plane extending midway across the lands62 and 63. These components balance the forces which tend to urge thecylinder block toward the pintle 104 in the region of the highpressurecontrol chamber.

The force which tends to move the cylinder block toward the pintle 104at the inner dead center position of a piston is balanced by thecorresponding component of the pressure field in the region of thatcutout which is located opposite such piston. That component of the lastmentioned pressure field which acts in the same direction as the forceacting to move the cylinder block toward the pintle 104 in the region ofa piston dwelling in its innermost position is automatically reduced(prior to being fully neutralized) due to the fact that the gap in theregion of the respective cutout increases with the result that thepressure field becomes weaker until the forces acting on the cylinderblock balance each other. This also neutralizes the forces acting on thepintle I04 because the latter takes up radial stresses acting on thecylinder block.

As a rule, pressure fields develop only in the region of those cutoutswhich communicate with the highpressure control chamber of the pintle,i.e., only such pressure fields exert a pronounced influence on thebalance of forces acting on the cylinder block. The pressure fieldswhich develop in the region of the cutouts in communication with thelow-pressure (suction) chamber are normally negligible. However, if thedirection of rotation of the cylinder block remains unchanged while thedirection of fluid flow changes the low-pressure chamber becomes thehigh-pressure chamber and vice versa. Due to aforedescribed symmetricdistribution of cutouts in the periphery of the pintle 4 or 104. theforces acting on the cylinder block are balanced again whereby thepreviously negligible pressure fields contribute significantly to abalancing of forces which act upon the cylinder block, and vice versa.

The combined area of relatively small sealing ribs 58-61, lands 62, 63and auxiliary sealing ribs 68, 69, 82, 83 suffices for satisfactoryguidance of the cylinder block and counteracts the unbalancedhydrostatic forces. At the same time, the losses due to friction areminimal.

FIG. 4 shows a further valve or pintlc 204 having two elongated controlchambers 86, 87, two lands 92, 93, and scaling ribs 88, 89 and 90, 91which respectively flank the control chambers 86, 87. The land 92 hasfour rectangular recesses or cutouts 94, 95, 96 and 97 of differentsizes. The smaller cutouts 95, 97 can communicate with the controlchamber 87 by way of successive ports l3 and associated grooves l4, l5,and the larger cutouts 94, 96 can communicate in the same way with thecontrol chamber 86. The larger outer cutouts 94, 96 are respectivelyflanked by auxiliary sealing ribs 98, 99. The cutouts 94, 96respectively communicate with channels or bores I00, 10] having inletsI, I01 which are respectively adjacent to the path of successive groovesl4, 15. The channels 95, 97 respectively include channels or extensions102, 103 located in the path of movement of successive grooves l4, l5.

When a port I3 travels along the land 92 from the control chamber 86toward the control chamber 87, the associated grooves l4. 15respectively communicate with the inlets 100. 101 so that the controlchamber 86 is in communication with the cutouts 94, 96 by way of therespective bores I00, 101. The port 13 thereupon begins to communicatewith a pilot notch [04 of the control chamber 87 shortly before thegrooves 14, I5 reach the extensions I02. 103 of the cutouts 95, 97. Theport 13 begins to communicate with the pilot notch I04 after the groovesl4, move beyond the inlets I00, 101. The grooves 14, 15 communicate withthe extensions 102, 103 while the corresponding port 13 communicateswith the control chamber 87.

The land 93 is identical with the land 92. It is provided with twosmaller recesses or cutouts I06, I08 having channels or extensions I11,I12 and with two larger recesses or cutouts 105, I07 communicating withchannels or bores 109, HO having inlets I09, I10. Successive grooves 14communicate first with the inlet 109' to thereby connect the controlchamber 87 with the cutout 105. and thereupon with the extension 111 tothereby connect the control chamber 86 with the cutout 106. Analogously,successive grooves 15 communicate first with the inlet to connect thecontrol chamber 87 with the cutout I07, and thereupon with the extension2 to connect the control chamber 86 with the cutout 108. The pilot notch113 of the control chamber 86 begins to communicate with a port 13 afterthe respective grooves 14, I5 advance beyond the inlets 109, I10, andthe port I3 communicates with the control chamber 86 while therespective grooves l4, l5 overlie the extensions ll], H2. The largerouter cutouts I05, 107 of the land 93 are flanked by auxiliary sealingribs 114, I15. It will be noted that the pilot notch 113 extends counterto the direction of rotation (arrow A), of the cylinder block.

The manner in which the pressure fields are built up in a machineembodying the pintle 204 of FIG. 4 is analogous to that described withreference to FIG. 2. If the cylinder block (not shown) rotates in thedirection indicated by arrow A, and if the control chamber 87 is thehigh-pressure chamber, a port 13 travels along the land 93 of the pintle204 when the corresponding piston is nearest to the axis of the pintle.The pressure fields in the region of the cutouts I05 and 107 developwhenever the grooves l4, 15 associated with a port 13 which is still incommunication with the high-pressure chamber 87 reach the inlets 109',110. Such pressure fields are capable of offering a substantialresistance to radial movement of the cylinder block toward the peripheryof the pintle 204, and are much more pronounced than the pressure fieldsin the region of cutouts 95, 97. The cutouts 95, 97 are locateddiametrically opposite the cutouts I05. 107 and intermittently receivepressurized fluid from the control chamber 87 by way of the pilot notch104, successive ports I3, associated grooves l4, l5 and the extensionsI02, 103. The pressure fields in the region of the cutouts I05, 107compensate for the force whiclh tends to move the cylinder block towardthe land 93 due to the fact that the piston sweeping past the land 93pressurizes the fluid in the respective cylinder bore. Moreover, thepressure fields in the region of cutouts I05, I07 counteract thepressure fields in the region of cutouts 95, 97. The intensity ofsuchpressure fields is adjusted automatically in that the gap between thepin'tle 204 and the cylinder block increases wherever the forces areunbalanced whereby the leakage of pressurized fluid increases and themagnitude of the respective pressure fields decreases accordingly. Byproperly dimensioning the cutouts in the lands 92, 93, one can achievean extensive balancing of forces and thus an accurate centering of thecylinder block on the pintle.

It will be noted that the larger cutouts 105, 107 in the land 93communicate with the high-pressure chamber 87 because a piston movespast the land 93 while it pressurizes the fluid in the respectivecylinder bore. If the control chamber 86 is the high-pressure chamber,the pistons move radially inwardly during travel toward the land 92 sothat pronounced pressure fields develop in the region of the largecutouts 94. 96. Thus, pronounced pressure fields are always establishedin the region of those larger cutouts which are in communication withsuccessive ports 13 while the respective pistons approach, reach andleave their inner dead-center positions. In this manner, one achieves ahighly satisfactory balancing of forces irrespective of the direction offluid transport, as long as the cylinder block rotates in the samedirection. Such balancing of forces renders it possible to greatlyreduce the combined area of surfaces (on the sealing ribs and lands) forguidance of the cylinder block which, in turn, results in a substantialreduction of losses due to friction.

The recesses or cutouts 94-97 and 105108 are located centrally of thelands 92, 93. as considered in the circumferential direction of thepintle 204.

FIGS. 5a and 5b illustrate a portion of a modified radial piston machinewith a presently preferred configuration of cylinder bores in a cylinderblock 120 which enhance the balancing of remaining forces acting uponthe cylinder block in the region of the high-pressure chamber in thevalve or pintle 121. The cylinder block 120 has an axial bore bounded byan internal surface 120 which surrounds the pintle 121. The cylinderbores 122 of the block 120 extend radially outwardly from the internalsurface 120. The pintle 121 has two control chambers 123, 124 which areseparated from each other by lands 123 (one shown in FIG. 5a).

Each cylinder bore 122 has an inner end portion or port 125 and thecylinder block 120 has internal shoulders 126 between the main portionsof the bores 122 and the respective ports 125. Each port 125communicates with a rectangular recess or cavity 127 which is machinedinto the internal surface 120 and extends in the circumferentialdirection of the pintle 121. The neighboring cavities 127 are separatedfrom each other by narrow webs 129. The width of a land 123 on thepintle 121 equals the distance between the centers of two neighboringports 125, as considered in the circumferential direction of the pintle.The length ofeach cavity 127 equals the width of a land 123 minus thewidth of a web 129, as considered in the circumferential direction ofthe pintle 121. As a rule, the length of a cavity 127 is between 8571and 95% of the width of a land 123'. The width of a cavity 127, asconsidered in the axial direction of the pintle 121. is selected inaxial direction of the pintle 121, is selected in such a way that thepressure field developing in the region of such cavity can counteractthe remaining force which develops in response to pressurization offluid in the respective bore 122.

When a cylinder bore 122 travels from the highpressure chamber (e.g.,control chamber 123) toward the low-pressure chamber and the respective'port 125 moves along the land 123' of FIG. 5a, the cavity 127 insuresthat the bore 122 continues to communicate with the high-pressurechamber. Consequently, the force which the fluid in the bore 122 exertsagainst the shoulder 126 and which tends to urge the cylinder block 120against the periphery of the pintle 121 remains intact as long as theadjacent portion ofthe internal surface 120 continues to overlie thehigh-pressure chamber 123. Such portion of the surface 120' is subjectedto the action of forces V,, which tend to move the cylinder block 120away from the pintle 121 and which are opposed by lluid pressure actingagainst the shoulder 126. In other words, that portion of the cylinderblock 120 which extends between the centers of two neighboring ports 125or between two neighboring webs 129 is acted upon simultaneously by afirst force (shoulder 126) tending to move the cylinder block toward thepintle 121 and by a second force which tends to move the cylinder blockaway from the pintle. The

second force acts upon that portion of the internal surface (in theregion of the respective port which continues to overlie thehigh-pressure chamber 123. Shortly after a cavity 127 moves into fullregister with the land 123', it begins to communicate with thelow-pressure chamber 124 so that the force which tends to move thecylinder block 120 away from the pintle 12] decreases simultaneouslywith the force which tends to move the cylinder block toward the pintle.

When a port 125 moves along the other land of the pintle 121 (on its wayfrom the low-pressure chamber 124 toward the high-pressure chamber 123),there develops a force which tends to move the cylinder block 120 awayfrom the pintle as soon as the adjacent portion of the internal surface121) begins to overlie the chamber 123. Since the length of a cavity 127closely approximates the width of a land 123' (ie, the distance betweenthe centers of two neighboring ports 125 minus the width of a web 129),the respective bore 122 begins to communicate with the high-pressurechamber 123 practically simultaneously with the generation of a forcewhich tends to move the cylinder block 120 away from the pintle 121,whereby the fluid acting on the corresponding shoulder 126 urges thecylinder block toward the pintle and balances the aforementionedseparating or lifting force. The two forces act along the same line butin opposite directions so that they can neutralize each other.

Each recess or cavity 127 includes two mirror symmetrical portions 128(sec particularly FlG. 512) one of which extends forwardly and the otherof which ex-' tends rearwardly of the respective port 125, as consideredin the direction of rotation of the cylinder block 120.

The preceding description indicates that the forces which tend to movethe cylinder block toward and away from the pintle neutralize each otherin the region of those cylinder bores where the pistons are in theprocess of changing the direction of their movement. The cavities 1277evidently do not influence such forces while they are in full registerwith the highpressure chamber of the pintle.

The improved pintle and cylinder block are susceptible of manyadditional modifications without departing from the spirit of theinvention. For example, the ports of the cylinder bores can beconfigurated in such away that the cavities 127 of FIGS. 5a and 5/) canbe dispensed with. Also, the cutouts in the lands of the pintle need nothave a rectangular or square shape, the extensions of the cavities canbe replaced by bores, and the bores can be replaced by extensions. Thecylinder block 120 of FIGS. 5a and 5b can be used in combination withthe pintle 4, 104 or 204.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featureswhich fairly constitute essential characteristics of the generic andspecific aspects of my contribution to the art and, therefore, suchadaptations should and are intended to be comprehended within themeaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by letters patent isset forth in the appended:

1. In a radial piston machine, a combination comprising a rotarycylinder block having a cylindrical external 13 surface and radiallyextending cylinder bores including end portions tcrminatins in saidinternal surface; and a valve having a cylindrical external surfacesurrounded by said internal surface, a high-pressure chamber and alow-pressure chamber provided in said external surface, said chambersbeing in register with and being swept seriatim by successive endportions when said block rotates relative to said valve and saidexternal surface including two portions constituting lands between saidchambers, said external surfaces further having at least two recesses ineach of said lands, offset in axial direction of said block relative tosaid chambers and respectively located to opposite sides of the path ofthe end portions of successive cylinder bores, each of said recessesbeing in temporary communication with that cylinder bore whose endportion travels in the region of the respective land.

2. A combination as defined in claim 1, wherein said internal surface isprovided with grooves, at least one for each cylinder bore and eachcommunicating with the respective cylinder bore, said cylinder boresbeing arranged to communicate with said recesses by way of therespective grooves.

3. A combination as defined in claim 1. wherein said recesses include afirst group of recesses in one of said lands and a second group ofrecesses in the other of said lands, each group of recesses including atleast one first recess which communicates with successive cylinder boreswhile the end portions of the respective cylinder bores simultaneouslycommunicate with one of said chambers and at least one second recesswhich communicates with successive cylinder bores while the end portionsof the respective cylinder bores communicate with the other ofsaidchambers, said lands further having first and second channels whichrespectively establish communication between said first and secondrecesses and successive cylinder bores, the distance be tween said firstchannels or said second channels, as considered in the circumferentialdirection of said valve, being a whole multiple of the distance betweenthe centers of the end portions of two neighboring cylinder bores insaid block.

4. A combination as defined in claim I, wherein said recesses include afirst and a second group respectively provided in the one and the otherof said lands and the recesses of each group include at least one firstrecess which communicates with successive cylinder bores while the endportions of the respective cylinder bores communicate with saidhigh-pressure chamber and at least one second recess which communicateswith successive cylinder bores while the end portions of the respectivecylinder bores communicate with said lowpressure chamber, the distancebetween said first recesses, as considered in the circumferentialdirection of said valve, being less than 180 degrees.

5. A combination as defined in claim 1, wherein said valve furthercomprises sealing ribs flanking said chambers and auxiliary sealing ribsflanking said recesses, said sealing ribs constituting with said landsthe sole means for guiding said internal surface while said cylinderblock rotates relative to said valve.

6. A combination as defined in claim 1, wherein said recesses include afirst and a second group of four recesses each respectively provided inthe one and the other of said lands, each of said groups including afirst pair of recesses which communicate with successive cylinder boresduring the last stage of communication of the corresponding end portionswith one of the chambers and a second pair of recesses which communicatewith successive cylinder bores during the initial stage of communicationof the corresponding ports with the other of said chambers.

7. A combination as defined in claim 6, wherein one pair of saidrecesses ofeach group is located behind the other pair of recesses ofthe respective group, as considcred in the direction of rotation of saidcylinder block.

8. A combination as defined :in claim 6, wherein one pair of recesses ofeach of said groups is nearer to the path of said end portions than theother pair of recesses of the respective group.

9. A combination as defined in claim 1, wherein said valve is furtherprovided with channels by means of which said recesses communicate withthe end portions of successive cylinder bores.

10. A combination as defined in claim 9, wherein at least some of saidchannels are bores.

11. A combination as defined in claim 9, wherein at least some of saidchannels are extensions of said recesses.

12. A combination as defined in claim I, wherein the recesses in each ofsaid lands include at least one first recess and at least one largersecond recess said second recesses being arranged to communicate withthose cylinder bores whose end portions simultaneously register withsaid high-pressure chamber,

13. A combination as defined in claim 12, wherein said recesses arelocated substantially centrally of the respective lands, as consideredin the circumferential direction of said valve.

14. In a radial piston machine, a combination comprising a rotarycylinder block [having a cylindrical internal surface and radiallyextending cylinder bores including end portions terminating in saidinternal surface; and a valve having a cylindrical external surfacesurrounded by said internal surface, a high-pressure chamber and alow-pressure chamber provided in said external surface, said chambersbeing swept seriatim by successive end portions when said block rotatesrelative to said valve and said external surface including two portionsconstituting lands between said chambers, each of said lands beingprovided with at least one recess adjacent to one side of the path ofthe end portions of successive cylinder bores, and with at least onesecond recess adjacent to the other side of said path, said internalsurface having a pair of grooves for each of said cylinder bores and thegrooves of each pair being in communication with the respective cylinderbores, one groove of each pair being .arranged to communicate with saidfirst recesses and the other groove of each pair being arranged tocommunicate with said second recesses when said cylinder block rotatesand said cylinder bores travel in the region of the respective lands.

1. In a radial piston machine, a combination comprising a rotarycylinder block having a cylindrical external surface and radiallyextending cylinder bores including end portions terminatins in saidinternal surface; and a valve having a cylindrical external surfacesurrounded by said internal surface, a high-pressure chamber and alow-pressure chamber provided in said external surface, said chambersbeing in register with and being swept seriatim by successive endportions when said block rotates relative to said valve and saidexternal surface including two portions constituting lAnds between saidchambers, said external surfaces further having at least two recesses ineach of said lands, offset in axial direction of said block relative tosaid chambers and respectively located to opposite sides of the path ofthe end portions of successive cylinder bores, each of said recessesbeing in temporary communication with that cylinder bore whose endportion travels in the region of the respective land.
 2. A combinationas defined in claim 1, wherein said internal surface is provided withgrooves, at least one for each cylinder bore and each communicating withthe respective cylinder bore, said cylinder bores being arranged tocommunicate with said recesses by way of the respective grooves.
 3. Acombination as defined in claim 1, wherein said recesses include a firstgroup of recesses in one of said lands and a second group of recesses inthe other of said lands, each group of recesses including at least onefirst recess which communicates with successive cylinder bores while theend portions of the respective cylinder bores simultaneously communicatewith one of said chambers and at least one second recess whichcommunicates with successive cylinder bores while the end portions ofthe respective cylinder bores communicate with the other of saidchambers, said lands further having first and second channels whichrespectively establish communication between said first and secondrecesses and successive cylinder bores, the distance between said firstchannels or said second channels, as considered in the circumferentialdirection of said valve, being a whole multiple of the distance betweenthe centers of the end portions of two neighboring cylinder bores insaid block.
 4. A combination as defined in claim 1, wherein saidrecesses include a first and a second group respectively provided in theone and the other of said lands and the recesses of each group includeat least one first recess which communicates with successive cylinderbores while the end portions of the respective cylinder borescommunicate with said high-pressure chamber and at least one secondrecess which communicates with successive cylinder bores while the endportions of the respective cylinder bores communicate with saidlow-pressure chamber, the distance between said first recesses, asconsidered in the circumferential direction of said valve, being lessthan 180 degrees.
 5. A combination as defined in claim 1, wherein saidvalve further comprises sealing ribs flanking said chambers andauxiliary sealing ribs flanking said recesses, said sealing ribsconstituting with said lands the sole means for guiding said internalsurface while said cylinder block rotates relative to said valve.
 6. Acombination as defined in claim 1, wherein said recesses include a firstand a second group of four recesses each respectively provided in theone and the other of said lands, each of said groups including a firstpair of recesses which communicate with successive cylinder bores duringthe last stage of communication of the corresponding end portions withone of the chambers and a second pair of recesses which communicate withsuccessive cylinder bores during the initial stage of communication ofthe corresponding ports with the other of said chambers.
 7. Acombination as defined in claim 6, wherein one pair of said recesses ofeach group is located behind the other pair of recesses of therespective group, as considered in the direction of rotation of saidcylinder block.
 8. A combination as defined in claim 6, wherein one pairof recesses of each of said groups is nearer to the path of said endportions than the other pair of recesses of the respective group.
 9. Acombination as defined in claim 1, wherein said valve is furtherprovided with channels by means of which said recesses communicate withthe end portions of successive cylinder bores.
 10. A combination asdefined in claim 9, wherein at least some of said channels are bores.11. A combInation as defined in claim 9, wherein at least some of saidchannels are extensions of said recesses.
 12. A combination as definedin claim 1, wherein the recesses in each of said lands include at leastone first recess and at least one larger second recess, said secondrecesses being arranged to communicate with those cylinder bores whoseend portions simultaneously register with said high-pressure chamber.13. A combination as defined in claim 12, wherein said recesses arelocated substantially centrally of the respective lands, as consideredin the circumferential direction of said valve.
 14. In a radial pistonmachine, a combination comprising a rotary cylinder block having acylindrical internal surface and radially extending cylinder boresincluding end portions terminating in said internal surface; and a valvehaving a cylindrical external surface surrounded by said internalsurface, a high-pressure chamber and a low-pressure chamber provided insaid external surface, said chambers being swept seriatim by successiveend portions when said block rotates relative to said valve and saidexternal surface including two portions constituting lands between saidchambers, each of said lands being provided with at least one recessadjacent to one side of the path of the end portions of successivecylinder bores, and with at least one second recess adjacent to theother side of said path, said internal surface having a pair of groovesfor each of said cylinder bores and the grooves of each pair being incommunication with the respective cylinder bores, one groove of eachpair being arranged to communicate with said first recesses and theother groove of each pair being arranged to communicate with said secondrecesses when said cylinder block rotates and said cylinder bores travelin the region of the respective lands.